Most modern consumer electronic devices have some form of handheld remote control. Recently, there has been much work in the voice command remote control area. For example, in an audio-video playback system a device can have a conventional handheld infrared remote control with a microphone built in for accepting voice commands and converting the command into an infrared signal that is transmitted to the device. Other techniques for voice command include multiple microphone systems in which one microphone senses the voice command and ambient noise, and another microphone picks up only ambient noise, allowing for isolation of the voice command through subtraction of the ambient signal.
Many techniques exist for reducing sensitivity to ambient noise. In voice command driven remote controlled devices, there exists the problem of isolating the ambient sound from the command. For example, U.S. Pat. No. 6,411,928 (Sanyo Electric) describes a method in which an electrical signal corresponding to ambient noise is used to set a threshold value in accordance with the level of the ambient noise. A voice signal applied to a microphone is cut out for processing if it exceeds the threshold value. In another voice-operated remote control system U.S. Pat. No. 5,267,323 (Pioneer Electronic Corp), a two-microphone system has one microphone receives a voice command and the other receiving the ambient noise. An ambient noise remover cancels an ambient noise component with an electric signal of the ambient noise picked up by the other microphone, leaving only the voice command component. In both of these cases, the ambient noise refers to sounds in the acoustic environment as well as sounds emitted by the device being controlled. When the sound level from the device is sufficiently loud, the ability for the system to recognize the voice command generally suffers, in part due to room reflections and other acoustic phenomena.